The present invention relates to a fast neutron nuclear reactor where the cooling of the core by extracting the calories released by nuclear fission is brought about by circulating a liquid metal.
The invention applies more particularly in the case of a reactor of the above type, a so-called integrated reactor, in which the volume of liquid metal, generally sodium, necessary for cooling the core is contained in an open vessel having a vertical axis called the main vessel suspended beneath a horizontal thick slab which closes a cavity containing said vessel and located in a concrete protective enclosure. The core of the reactor comprising juxtaposed fuel assemblies rests on a girder which also supports a second vessel or inner vessel having its upper end open and surrounding the core and mounted in the main vessel. In the annular space defined between the side walls of the main vessel and the inner vessel are provided heat exchangers and circulating pumps, so-called primary pumps, traversing vertical passages provided in the upper slab and which pass into the sodium volume. The hot sodium from the core, after passing through the latter from bottom to top, is collected in the inner vessel. It then leaves the latter and penetrates the exchangers where the calories obtained are transferred to a secondary fluid, the cold sodium emanating from the exchangers in the space between the two vessels being taken up by the circulating pumps and is then returned under a suitable pressure beneath the core girder and then again passes through the core.
In a special construction of a fast integrated reactor of the type indicated hereinbefore, on leaving the core located in the inner vessel the hot sodium is caused to circulate between the core and the side wall of said vessel and is then removed from the latter by tubes directly connected at the base of each exchanger with a central duct provided in the latter. Advantageously an arrangement of this type can be in accordance with that described and claimed in French patent application 760,982 of Mar. 29, 1976 entitled "Fast neutron nuclear reactor" filed in the name of the Commissariat a l'Energie Atomique.
However, in the case of the constructions described hereinbefore the hot sodium collected in the upper part of the inner vessel partly stagnates due to the fact that the tubes are located in the lower part of said vessel supplying the sodium to the exchangers. If a fault or irregularity occurs in the reactor due to the unavailability of the secondary circuits of the exchangers or the unavailability of both said secondary circuits and the primary pumps, it is necessary to be able to remove the residual heat from the reactor.